Anchorage-independent growth of pocket protein-deficient murine fibroblasts requires bypass of G2 arrest and can be accomplished by expression of TBX2.
Mouse embryonic fibroblasts (MEFs) deficient for pocket proteins (i.e., pRB/p107-, pRB/p130-, or pRB/p107/p130-deficient MEFs) have lost proper G(1) control and are refractory to Ras(V12)-induced senescence. However, pocket protein-deficient MEFs expressing Ras(V12) were unable to exhibit anchorage-independent growth or to form tumors in nude mice. We show that depending on the level of pocket proteins, loss of adhesion induces G(1) and G(2) arrest, which could be alleviated by overexpression of the TBX2 oncogene. TBX2-induced transformation occurred only in the absence of pocket proteins and could be attributed to downregulation of the p53/p21(CIP1) pathway. Our results show that a balance between the pocket protein and p53 pathways determines the level of transformation of MEFs by regulating cyclin-dependent kinase activities. Since transformation of human fibroblasts also requires ablation of both pathways, our results imply that the mechanisms underlying transformation of human and mouse cells are not as different as previously claimed.
Vormer
Tinke L
TL
Division of Molecular Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Foijer
Floris
F
Wielders
Camiel L C
CL
te Riele
Hein
H
D000818:Animals; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology*; D016195:G2 Phase / Q000502:physiology*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008819:Mice, Nude; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D050720:Retinoblastoma-Like Protein p107 / Q000235:genetics / Q000378:metabolism*; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D020033:Protein Isoforms; D016160:Retinoblastoma Protein; D050720:Retinoblastoma-Like Protein p107; C097348:T-Box Domain Protein 2; D020825:T-Box Domain Proteins; D016159:Tumor Suppressor Protein p53; D018631:ras Proteins